1. Field of the Invention
This invention relates to fuel cell electrodes of the type comprising porous carbon with high surface area metal or alloy thereof supported thereon. Such electrodes have been commonly used as diffusion electrodes in low temperature fuel cells which operate at temperatures from ambient to about 200.degree. or 300.degree. C.
Such fuel cells provide oxidation of an externally supplied fuel at the anode making electrons available for flow in an external circuit. The oxidation of the fuel results in production or neutralization of ions at the anode which pass through the electrolyte to or from the cathode where they are neutralized or created by oxygen and electrons. Many fuel cells utilize diffusion electrodes permitting fuel gas or oxygen or air to diffuse into the interior of the pores of the electrode from one side, while the electrolyte penetrates the pores from the other side. The chemical and catalytic action takes place at the interface between the electrolyte, the reacting gas and the electrode. The stability of the electrode and its associated catalyst is an important aspect in the successful and practical operation of a fuel cell. The present invention provides stabilization of such catalysts during operation of fuel cells of the type having at least one electrode comprising porous carbon with high surface area metal or alloy thereof supported thereon.
2. Description of the Prior Art
Typical fuel cells are well known in the art and are generally described in a number of references such as "Fuel Cells," D. P. Gregory, M & B Monograph CE/7, Mills & Boon Limited, London (1972) and "Handbook of Fuel Cell Techology," Carl Berger, editor, Prentice-Hall, Inc., Englewood Cliffs, N.J. (1968).
Fuel cell electrodes of the type having porous carbon with high surface area metal or alloys thereof supported thereon have been known in the art as exemplified by U.S. Pat. No. 3,857,737 relating to a noble metal catalyst such as platinum deposited on particles of an inert carrier such as carbon. The catalytic activity of platinum supported on carbon fabricated into Teflon-bonded diffusion electrodes for phosphoric acid fuel cells has been known as exemplified by "The Catalytic Activity of Platinum Supported on Carbon for Electrochemical Oxygen Reduction in Phosphoric Acid," H. R. Kunz and G. A. Gruver, Journal of the Electrochemical Society, Vol. 122, No. 10, pp 1279-1287 (1975).
The prior art has recognized the desirability of stability of the electrocatalysts during extended periods of fuel cell operation. One attempt to obtain such stability is described in U.S. Pat. No. 4,090,978 teaching use of carbonaceous pyropolymers in the preparation of an electrocatalyst.